Trump has boasted about taking advantage of the tax code to pay as little as possible, but he's also made targeting those loopholes and the people and companies who use them a big part of his presidential campaign.

He's been increasingly reluctant to reveal his current tax returns, first claiming an Internal Revenue Service audit prevented him from disclosing them. According to several outlets, an audit doesn't legally prevent him from disclosing his past returns.

GALLERY: Five fun financial facts about Donald Trump:

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Five fun financial facts: Donald Trump (Moneytips.com)

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The last time Donald Trump's tax returns went public, he paid $0

1. Of the 515 companies that Trump oversees, 268 are branded with his name.